Bi-directional and adjustable current source

ABSTRACT

A Bi-Directional and Adjustable Current Source (“BACS”) for providing an input voltage to a mute/standby control pin of a power stage integrated circuit (“IC”) of an amplifier input with a voltage signal that is linear, where an output of the BACS and the input to the control pin are shunted with a capacitor, is described. The BACS may include a first switch in signal communication with a high voltage reference and a first current source in signal communication with the first switch. The BACS may also include a second switch in signal communication with a low voltage reference and a second current source in signal communication with the second switch. The BACS may further include a directional current element in signal communication with both the first current source, the second current source, the output of the BACS, the input to the control pin, and the capacitor, where the directional current element is configured to prevent current flow from the output BACS to the first current source.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. Non-ProvisionalApplication entitled “Bi-Directional and Adjustable Current Source,”application Ser. No. 12/391,133, filed Feb. 23, 2009, which applicationis incorporated into this application by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates, in general, to electronic circuits and, inparticular, to electronic circuits that control abrupt transients duringamplifier power-up and power-down operations.

2. Related Art

In conventional amplifiers, electronic operations that either power-upor power-down an amplifier may cause abrupt transients that surge theoutput of the amplifier causing unpleasant audible noises (commonlyreferred to as a “pops”) when the output of the amplifier is utilized todrive a coupled load (such as, for example, an audio speaker orheadset). Unfortunately, this situation is a problem because not onlyare these “pops” unpleasant to a listener but they may also damage thecoupled load because the abrupt transients may surge the output of theamplifier to a power level capable of damaging either the audio speakersor headset.

In an automotive environment, as an example, this problem is difficultto solve due to multiple factors such as: a varying system voltage; asound proofed quiet cabin; and listeners located in close proximity tomultiple, highly sensitive speakers. Unfortunately, known techniques forattempting to solve this problem adversely affect other aspects of thesystem.

As an example, a conventional attempt to partially solve this problemhas been to improve the transients by correspondingly attempting toimprove the transition performance of the amplifier by graduallypowering down the power state of the amplifier in a controlled manner.Typically, this is done by utilizing an RC circuit that provides anexponential voltage curve to the amplifier in order to control thepower-down and power-up operations of the amplifier. Unfortunately, thisexponential voltage curve is non-linear and, therefore, the resultingpowering-down and powering-up times of the amplifier are different.

As a result, there is a need for a new circuit and method capable ofcontrolling the resulting abrupt transients caused by either powering upor powering down an amplifier without utilizing a circuit that providesthe amplifier with a voltage signal that is characterized by anon-linear voltage curve.

SUMMARY

A Bi-Directional and Adjustable Current Source (“BACS”) for providing aninput voltage to a mute/standby control pin of a power stage integratedcircuit (“IC”) of an amplifier that is linear, where an output of theBACS and the input voltage are shunted with a capacitor, is described.The BACS may include a first switch in signal communication with a highvoltage reference and a first current source in signal communicationwith the first switch. The BACS may also include a second switch insignal communication with a low voltage reference and a second currentsource in signal communication with the second switch. The BACS mayfurther include a directional current element in signal communicationwith both the first current source, the second current source, theoutput of the BACS, the amplifier input, and the capacitor, where thedirectional current element is configured to prevent current flow fromthe output BACS to the first current source.

Other systems, methods, features and advantages of the invention will beor will become apparent to one with skill in the art upon examination ofthe following figures and detailed description. It is intended that allsuch additional systems, methods, features and advantages be includedwithin this description, be within the scope of the invention, and beprotected by the accompanying claims.

BRIEF DESCRIPTION OF THE FIGURES

The components in the figures are not necessarily to scale, emphasisinstead being placed upon illustrating the principles of the invention.In the figures, like reference numerals designate corresponding partsthroughout the different views.

FIG. 1 is a circuit diagram showing an example of an implementation of aBi-Directional and Adjustable Current Source (“BACS”).

FIG. 2 is a circuit diagram showing an example of an implementation ofthe BACS shown in FIG. 1 utilizing both bipolar junction and fieldeffect transistors.

FIG. 3 is a plot of voltage versus time for the BACS.

FIG. 4 is a circuit diagram showing an example of an implementation of aBACS coupled to a mute/standby control pin of a power stage integratedcircuit (IC) of an amplifier.

DETAILED DESCRIPTION

A Bi-Directional and Adjustable Current Source (“BACS”) for providing amute/standby control pin of a power stage integrated circuit (“IC”) ofan amplifier with a voltage signal that is linear is described. Ingeneral, the BACS operates by controlling the current that charges acapacitor that is shunted on the output of the BACS so as to provide alinear voltage with a constant slope (referred to as a “voltage ramp”)at the output of the BACS. The output of the BACS is in signalcommunication with the control pin of the power IC of the amplifier. TheBACS produces linear charging and discharging voltage ramps and mayproduce equal charging and discharging times in the power-down andpower-up operations.

In FIG. 1, a circuit diagram of an example of an implementation of aBACS 100 is shown. The BACS 100 may include a first current source 102,second current source 104, directional current element 106, capacitor C108 (referred to as a “ramp capacitor”), first switch 110, and secondswitch 112. As an example, the first switch 110 may be in signalcommunication the first current source 102 via signal path 114. Thedirectional current element 106 may be in signal communication with thefirst current source 102, second current source 104, and capacitor 108via signal paths 116, 118, 120, and 122, respectively, where signalpaths 118, 120, and 122 are in signal communication via a signal node124. The second current source 104 may be in signal communication withthe second switch 112 via signal path 126. The second switch 112 andramp capacitor 108 may be in signal communication with low-voltagereference (for example, a zero-potential voltage reference such asground) 128 via signal paths 130 and 132, respectively. The BACS 100 mayalso be in signal communication with a coupled load 133, which may be,for example, an amplifier or more specifically, as shown in FIG. 4, amute/standby control pin of the power IC of an amplifier, at signal node124.

As an example, the directional current element 106 may be a diode. Theramp capacitor 108 may be an on-chip capacitor or an off-chip capacitorand may be formed of one or plural capacitors. The ramp capacitor 108may have a constant capacitance value or a varying capacitance value. Avarying capacitance value of the ramp capacitor 108 may be obtained byany method of varying a capacitance of a capacitor including, but notlimited to, when the ramp capacitor 108 is an off-chip capacitor,setting the capacitance of the ramp capacitor 108 at a selected value bychoosing the off-chip capacitor with an appropriate capacitance valueand, when the ramp capacitor 108 is formed of plural capacitors coupledvia switches, varying the capacitance of the ramp capacitor 108 byopening and closing switches between the capacitors to achieve a desiredcombinative capacitance value.

It is appreciated by those skilled in the art that the circuits,components, modules, and/or devices of the BACS 100 are described asbeing in signal communication with each other, where signalcommunication refers to any type of communication and/or connectionbetween the circuits, components, modules, and/or devices that allows acircuit, component, module, and/or device to pass and/or receive signalsand/or information from another circuit, component, module, and/ordevice. The communication and/or connection may be along any signal pathbetween the circuits, components, modules, and/or devices that allowssignals and/or information to pass from one circuit, component, module,and/or device to another and includes wireless or wired signal paths.The signal paths may be physical such as, for example, conductive wires,electromagnetic wave guides, attached and/or electromagnetic ormechanically coupled terminals, semi-conductive or dielectric materialsor devices, or other similar physical connections or couplings.Additionally, signal paths may be non-physical such as free-space (inthe case of electromagnetic propagation) or information paths throughdigital components where communication information is passed from onecircuit, component, module, and/or device to another in varying digitalformats without passing through a direct electromagnetic connection.

In an example of operation, the BACS 100 may perform as a voltageregulator that produces an output voltage V_(out) 134 that has a linearvoltage ramp that is caused by a constant current charging the rampcapacitor 108 at the signal node 124. The output voltage V_(out) 134 maybe used to drive the input of the load 133 that is in signalcommunication with the signal node 124. By utilizing the linear voltageramp of output voltage V_(out) 134, which may be ramped up or down at acontrolled rate of change, an output (not shown) of the load may havelittle or no abrupt transient voltage signal components.

In this example, the first switch 110 may be in signal communicationwith a high-voltage reference V_(S) 135 (such as, for example, a sourcevoltage). The capacitance of the ramp capacitor 108 may be varied beforeor during an operation of the BACS 100, which allows the rate of changein the capacitor voltage (also known as the ramp voltage, which is equalto the output voltage V_(out) 134) to be varied before or during theoperation of the BACS 100 while the capacitor voltage V_(out) 134 isbeing ramped up or ramped down.

As an example of operation, the BACS 100 is configured to operate in twomodes that are the charge-mode and discharge-mode. If either the firstswitch 110 or second switch 112 is closed, the resulting output voltageV_(out) 134 at the signal node 124 may be ramped up or down at aconstant or varying voltage change rate.

In the charge-mode, the first switch 110 is closed, the second switch112 is open, and the first current source 102 produces the chargecurrent I₁ 136 that flows through the directional current element 106 tothe signal node 124. Most of the charge current I₁ 136 then flowsthrough the capacitor 108 as a capacitor current I_(C) 138. Thecapacitor current I_(C) 138 charges the capacitor 108 and produces theramp voltage V_(cp) 136 across the capacitor 108 where the ramp voltageV_(cp) 136 is equal to the output voltage signal V_(out) 134.

In the charge-mode, if, for example, the first current source 102 is on,the first switch 110 is closed, and the second switch 112 is open, thefirst current source 102 produces a constant charge current I₁ 136 thatflows through the directional current element 106 into signal node 124and charges the ramp capacitor 108 as ramp current I_(C) 138. In thisexample, the ramp current I_(C) 138 is equal to the constant chargecurrent I₁ 136 because no current flows through the second currentsource 104 because the open second switch 112 operates as an electricalopen circuit that does not allow current to flow from the second currentsource 104.

In this example, assuming the low-voltage reference 128 is an electricalground having a potential voltage of zero, the value of the ramp voltageV_(out) 134 at signal node 124, as a function of time, is described bythe following equation:

${V_{out}(t)} = {\frac{1}{C}{\int{{I_{C}(t)}{\mathbb{d}t}}}}$where I_(C) (t) is the ramp current I_(C) 138 as a function of time “t”and C is the capacitance value of the ramp capacitor 108. Since the rampcurrent I_(C) 138 has a constant value because it is equal to theconstant charge current I₁ 136, the above equation simplifies to

${V_{out}(t)} = {\frac{I_{C}t}{C} = {\frac{I_{1}t}{C}.}}$As such, the ramp voltage V_(out) 134, as a function of time whencharging the ramp capacitor 108, is a linear response that ramps upversus time when the first switch 110 is closed, the first currentsource 102 is on, and the second switch 112 is open.

Alternatively, in the discharge-mode, if, for example, the secondcurrent source 104 is on, the first switch 110 is open, and the secondswitch 112 is closed, the second current source 104 operates as acurrent sink producing a constant discharge current I₂ 140 that flowsfrom the signal node 124 to the low-voltage reference 128. In thisexample, the ramp capacitor 108 discharges and produces ramp currentI_(C) 138 that flows from the ramp capacitor 108 to the signal node 124.The ramp current I_(C) 138 is equal to the constant discharge current I₂140 because no current flows through the directional current element 106because it only allows current flow in the opposite direction.Additionally, even if some discharge current were capable of flowing inthe opposite direction of the directional element 106, the first switch110 would not allow current flow through the first current source 102because the open first switch 110 operates as an electrical open circuitthat does not allow current to flow from the first current source 102.Therefore, in this example, the ramp current I_(C) 138 is equal to theconstant discharge current I₂ 140.

Again, assuming the low-voltage reference 128 is an electrical groundhaving a potential voltage of zero, the value of the ramp voltageV_(out) 134 at signal node 124, as a function of time, is described bythe following equation:

${V_{out}(t)} = {\frac{1}{C}{\int{{I_{C}(t)}{{\mathbb{d}t}.}}}}$Since the ramp current I_(C) 138 has a constant value because it isequal to the constant discharge current I₂ 140, the above equationsimplifies to

${V_{out}(t)} = {\frac{I_{C}t}{C} = {\frac{I_{1}t}{C}.}}$As such, the ramp voltage V_(out) 134, as a function of time whendischarging the ramp capacitor 108, is a linear response that ramps downversus time when the first switch 110 is open, the second current source104 is on, and the second switch 112 is closed.

The output voltage signal V_(out) 134 may be utilized by the load 133 togenerate a load output (not shown). In the case of the load 133 beingthe control pin of a power IC, output voltage signal V_(out) 134 may beutilized to gradually mute and unmute the power stage of an amplifier ina controlled manner, the mute and unmute control lines of the poweramplifier being gradually driven to a specified voltage threshold. Byutilizing the ramp voltage V_(out) 134 (which may be ramped-up or downat a controlled rate of change), the load output may produce an outputsignal (not shown) that has small or even non-existent abrupt transientvoltage signal components. Because the constant currents I₁ 136 and I₂140 may be either equal or different, the rate of a change in themagnitude of the ramp voltage V_(out) 134 will be constant while it isbeing ramped up or down.

In FIG. 2, a circuit diagram of an example of an implementation of theBACS 200 utilizing both bipolar junction (“BJT”) and field effecttransistors (“FETs”) is shown. In this example, the BACS 200 may includethe directional current element 106, a current driver section 202, andcurrent sink section 204. The current driver section 202 may be anexample of an architectural implementation of the first switch 110 andfirst current source shown 102 shown in FIG. 1. Similarly, the currentsink section 204 may be an example of an architectural implementation ofthe second switch 112 and second current source shown 104 shown inFIG. 1. The BACS 200 may include transistors Q₁ 206, Q₂ 208, Q₃ 210, Q₄212, Q₅ 214, and Q₆ 216; and resistors R₁ 218, R₂ 220, R₃ 222 and R₄224.

In this example, the current driver section 202 may include BJTtransistors Q₁ 206 and Q₂ 208, FET transistor Q₄ 212, and resistors R₁218 and R₃ 222. The transistor Q₂ 208 may be in signal communicationwith transistors Q₁ 206 and Q₄ 212 and resistor R₁ 218 via signal paths226, 228, and 230, respectively. The transistor Q₁ 206 is in signalcommunication with a Mute_Control input 232 and ground 236 via signalpaths 234 and 238 and resistor R₁ 218 is in signal communication withground 236. Resistor R₃ 222 is in signal communication with the drain240 and gate 242 of FET transistor Q₄ 212 and directional currentelement 106 via signal paths 244, 246, and 248, respectively. Thetransistor Q₂ 208 may receive a source voltage V_(S) 250, where thesource voltage V_(S) 250 may be equal to the high-voltage referenceV_(S) 135 shown in FIG. 1.

Similarly, the current sink section 204 may include BJT transistor Q₃210, FET transistors Q₅ 214 and Q₆ 216, and resistors R₂ 220 and R₄ 224.FET transistor Q₆ 216 may be in signal communication with BJT transistorQ₃ 210, gate 249 of FET transistor Q₅ 214, resistors R₂ 220 and R₄ 224,and ground 236 via signal paths 250, 256, 252, 254, and 258,respectively. The transistor Q₃ 210 is also in signal communication withthe Mute_Control input 232 and ground 236 via signal paths 260 and 262,respectively. FET transistor Q₅ 214 may be in signal communication withresistor R₄ 224 via signal path 264. Additionally, FET transistor Q₅ 214may be in signal communication with the directional current element 106and ramp capacitor 108 via signal node 124. The resistor R₂ 220 may alsoreceive the source voltage V_(s) 250, where the source voltage V_(S) 250may be equal to the high-voltage reference V_(S) 135 shown in FIG. 1.

In the charging mode, transistors Q₁ 206, Q₂ 208, and Q₄ 212 control thecharging of the ramp capacitor C1 108. When a Mute_Control 232 input isa logic “HI” (i.e., it powers up both Q₁ 206 and Q₃ 210), bothtransistors Q₁ 206 and Q₃ 210 turn on. Transistor Q₃ 210 holds offtransistor Q₆ 216, so it conducts no current. Transistor Q₁ 206 turns ontransistor Q₂ 208, which starts sinking current into transistor Q₄ 212and resistor R₁ 218. The gate 242 of FET transistor Q4 is wired suchthat the current flow through Q₄ 212 is controlled by the value ofresistor R₃ 222. Varying the value of R₃ 222 will vary thegate-to-source voltage (“V_(gs)”) of FET transistor Q₄ 212 which setsthe bias point. The constant charging current I₁ 120 flows through thedirectional current element 106 and charges the ramp capacitor 108,providing a linear voltage increase of V_(out) 134 over time at signalnode 124.

Alternatively, in the discharging mode, when Mute_Control 232 is a logic“LOW” (i.e., it does not power up both Q₁ 206 and Q₃ 210), bothtransistors Q₁ 206 and Q₃ 210 are turned off. Transistor Q₆ 216 isturned on by the pull-up resistor R₂ 220, which starts sinking currentout of transistor Q₅ 214 through R₄. Similarly to the case above, thegate 249 of FET transistor Q₅ 214 is wired such that the current flowthrough FET transistor Q₅ 214 is controlled by the value of resistor R₄224. The constant discharging current I₂ 124 flows through Q₅ 214 and Q₆216 discharging the ramp capacitor 108. This process provides a linearvoltage decrease of V_(out) 134 over time at the signal node 124. Inthis example of an implementation, transistors Q₄ 212 and Q₅ 214 shouldideally be the same, while R₄ 224, R₃ 222, and ramp capacitor 108 may beadjusted independently to set the slope of the time varying voltage rampof V_(out) 134 at the signal node 124.

FIG. 3 is a plot 300 of an example of a voltage curve 302 of the rampvoltage V_(out) 134 as function of time. In this example, from time tequals 0 to time t₁, the BACS 200 charges the ramp capacitor 108 and thevoltage curve 302 shows a constant positive slope that rises fromV_(out) (0) to V_(out) (t₁). From time t equals t₁ to time t₂, the rampcapacitor 108 is fully charged and the voltage curve 302 shows aconstant voltage of V_(out) (t₁). From time t equals t₂ to time t₃, theBACS 200 discharges the ramp capacitor 108 and the voltage curve 302shows a constant negative slope that drops from V_(out) (t₁) to V_(out)(0). Lastly, from time t equals t₃ to time t₄, the ramp capacitor 108 isfully discharged and the voltage curve 302 shows a constant voltage ofV_(out) (0).

FIG. 4 shows a circuit diagram of an example of an implementation of theBACS shown in FIG. 2 coupled to the control pin of a power stage IC. Inthis example 400, the BACS 410 utilizes both bipolar junction (“BJT”)and field effect transistors (“FETs”) and in the charging mode, providesa linear voltage increase of over time at the input control pin of thepower IC 420, and in the discharging mode, alternatively, provides alinear voltage decrease over time at the control pin. The charging ordischarging mode is selected at the POWERIC_UNMUTE_CONTROL_SIG pin 412.

While various embodiments of the invention have been described, it willbe apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible that are within the scopeof this invention.

1. A Bi-Directional and Adjustable Current Source (“BACS”) for providingan input voltage to a mute/standby control pin of a power stageintegrated circuit (“IC”) of an amplifier input with a voltage signalthat is linear, where an output of the BACS and the input to the controlpin are shunted with a capacitor, the BACS comprising: a first switch insignal communication with a high-voltage reference; a first currentsource in signal communication with the first switch; a second switch insignal communication with a low-voltage reference; a second currentsource in signal communication with the second switch; and a directionalcurrent element in signal communication with both the first currentsource, the second current source, the output of the BACS, the input tothe control pin, and the capacitor, wherein the directional currentelement is configured to prevent current flow from the output BACS tothe first current source.
 2. The BACS of claim 1, wherein thedirectional current element is a diode.
 3. The BACS of claim 1, whereinthe first switch includes a transistor configured to act as a switchingelement.
 4. The BACS of claim 3, wherein the first current sourceincludes a transistor configured to act as a current regulator.
 5. TheBACS of claim 1, wherein the second switch includes a transistorconfigured to act as a switching element.
 6. The BACS of claim 5,wherein the second current source includes a transistor configured toact as a current regulator.
 7. A method for providing an input voltageto a mute/standby control pin of a power stage IC of an amplifier inputwith a voltage signal that is linear utilizing a Bi-Directional andAdjustable Current Source (“BACS”) and a shunt capacitor, the methodcomprising: generating a first linear voltage signal when the shuntcapacitor is charging; and generating a second linear voltage signalwhen the shunt capacitor is discharging.
 8. The method of claim 7,wherein generating a first linear voltage signal includes providing acharge current from a first current source to the shunt capacitor via adirectional current element.
 9. The method of claim 8, whereingenerating a first linear voltage signal includes utilizing a diode asthe directional current element.
 10. The method of claim 9, whereingenerating a first linear voltage signal includes closing a firstswitching element in signal communication with the first current source.11. The method of claim 7, wherein generating a second linear voltagesignal includes sinking a discharge current from the shunt capacitor toa second current.
 12. The method of claim 11, wherein generating asecond linear voltage signal includes closing a second switching elementin signal communication with the second current source.
 13. ABi-Directional and Adjustable Current Source (“BACS”) for providing aninput voltage to a mute/standby control pin of a power stage IC of anamplifier input with a voltage signal that is linear, where an output ofthe BACS and the amplifier input to the control pin are shunted with acapacitor, the BACS comprising: means for generating a first linearvoltage signal when the shunt capacitor is charging; and means forgenerating a second linear voltage signal when the shunt capacitor isdischarging.
 14. The BACS of claim 13, wherein the means for generatinga second linear voltage signal when the shunt capacitor is dischargingincludes: a second switch in signal communication with a low-voltagereference; a second current source in signal communication with thesecond switch; and, wherein means for generating a first linear voltagesignal includes: a first switch in signal communication with ahigh-voltage reference; a first current source in signal communicationwith the first switch; and a directional current element in signalcommunication with both the first current source, the second currentsource, the output of the BACS, the input to the control pin, and thecapacitor, wherein the directional current element is configured toprevent current flow from the output BACS to the first current source.15. The BACS of claim 14, wherein the directional current element is adiode.
 16. The BACS of claim 14, wherein the first switch includes atransistor configured to act as a switching element.
 17. The BACS ofclaim 16, wherein the first current source includes a transistorconfigured to act as a current regulator.
 18. The BACS of claim 14,wherein the second switch includes a transistor configured to act as aswitching element.
 19. The BACS of claim 18, wherein the second currentsource includes a transistor configured to act as a current regulator.